6 Protection and Restoration in InternetA well defined set of restoration techniques already exists in the upper electronic layers:ATM/MPLSIPTCPRestoration speeds in different layers:BGP-4: 15 – 30 minutesOSPF: 10 seconds to minutesSONET: 50 millisecondsOptical Mesh: currently hundred milliseconds to minutes

7 Why Optical Layer ProtectionRestoration in the upper layers is slow and require intensive signalingOn contrary 50-ms range when automatic protection schemes are implement in the optical transport layer.Purpose of performing restoration in the optical layer:To decrease the outage time by exploiting fast rerouting of the failed connection.Main problem in adding protection function in a new layer:Instability due to duplication of functions.Need the merging of DWDM and electronic transport layer control and management.

8 Why Optical Layer Protection?Advantages.Speed.Efficiency.LimitationDetection of all faults not possible.(3R).Protects traffic in units of light paths.Race conditions when optical and client layer both try to protect against same failure.

10 Protection in Ring Network1+1 Path ProtectionUsed in access rings for traffic aggregation into central office1:1 Span and Line ProtectionUsed in metropolitan or long- haul rings1:1 Line ProtectionUsed for interoffice rings

11 Protection in Mesh NetworksNetwork planning and survivability designDisjoint path idea: service working route and its backup route are topologically diverse.Lightpaths of a logical topology can withstand physical link failures.Working PathBackup Path

12 Reactive / Proactive Reactive ProactiveA search is initiated to find a new lightpath which does not use the failed components after the failure happens.It can not guarantee successful recovery,Longer restoration timeProactiveBackup lightpaths are identified and resources are reserved at the time of establishing the primary lightpath itself.100 percent restorationFaster recoveryTaxonomy

13 Path Protection / Line ProtectionPath Switching: restoration is handled by the source and the destination.Line Switching: restoration is handled by the nodes adjacent to the failure.Line Protection.Normal OperationLine Switching: restoration is handled by the nodes adjacent to the failure Span Protection: if additional fiber is available.

14 1+1 ProtectionTraffic is sent over two parallel paths, and the destination selects a better one.In case of failure, the destination switch onto the other path.Pros: simple for implementation and fast restorationCons: waste of bandwidth

16 Shared ProtectionNormal Operation1:N ProtectionIn Case of FailureBackup fibers are used for protection of multiple linksAssume independent failure and handle single failure.The capacity reserved for protection is greatly reduced.

17 Multiplexing TechniquesPrimary Backup MultiplexingUsed in a dynamic traffic scenario, to further improve resource utilization.Allows a wavelength channel to be shared by a primary and one or more backup paths.By doing so, the blocking probability of demands decreases at the expense of reduced restoration guarantee. (An increased number of lightpaths can be established)A lightpath loses its recoverability when a channel on its backup lightpath is used by some other primary lightpath.It regains its recoverability when the other primary lightpath terminates.

18 Survivability Design: Joint Optimization ProblemProblem DescriptionGiven a network in terms of nodes (WXCs) and links, and a set of point-to-point demands, find both the primary lightpath and the backup lightpath for each demand so that the total required network capacity is minimized.NotationN: the set of nodes;L: the set of links;D: the set of demandsCij: the capacity weight for link (ij)Wij: the capacity requirement on link (ij) in terms of # of wavelengthObjectiveMinimize

25 ConclusionDifferent resilience schemes applicable in optical network have been discussed.Network planning and topology design for survivability is computationally intractable and faster heuristic solutions are needed.Multi-layer restoration is a hot point in current optical survivability research.Joint IP/optical restoration mechanism is the trend in next generation optical network.